This invention relates to an electrohydraulic vehicle with energy regeneration.
Vehicles with electrical drive are known from the prior art and they have a variable speed obtained by connecting to the electrical motor a variable-speed drive unit which, using direct or alternating current, will generate the signals necessary for control of an ac or dc electrical motor to obtain variable rpm of this motor. It is well known that optimum performance of this device is obtained when the motor is running at the nominal rpm; at other rpm performance is less than this optimum. Likewise, in vehicles with closed loop hydrostatic transmission, it is known in the prior art that the motors generally used are of the fixed displacement type, thereby causing incompatibility between the necessary (possible) flow rate and the pressure range for which they were designed, and not allowing them to reach high-vehicle speeds, while having a size adequate to provide the maximum torque necessary for starting out or climbing a steep hill.
The first object of the invention is therefore a vehicle with electrohydraulic drive which optimizes the operating conditions of the electrical motor powered by a battery, and on the other hand, obtaining both a high starting torque when this is necessary and speeds sufficient to allow the vehicle to speed without having to overdimension the hydraulic components.
This object is attained in a first embodiment by the fact that the vehicle has a battery powering an electrical motor when the vehicle is moving at its nominal speed in order to drive, at constant speed, a variable displacement hydraulic pump which is electronically controlled and managed by a circuit which monitors, manages and controls the angle of the cam plate which controls the variable displacement of the axial piston hydraulic pump which is connected in closed circuit via lines to at least one variable displacement hydraulic motor with a displacement which is monitored and controlled-hydraulically within a range limited by the maximum displacement and a non-zero minimum displacement, said hydraulic motor indirectly driving one or more wheels of the vehicle.
This object is attained in a second embodiment by the fact that the vehicle has battery (61) powering electric motor (60), said electric motor operating when the vehicle is moving at its nominal speed to drive, at a constant speed, variable displacement hydraulic pump (4) controlled and managed electronically by circuit (9) which monitors, manages and controls the angle of the cam plate which controls the variable displacement of hydraulic pump (4) which is connected in a closed circuit via lines to a variable displacement assembly of hydraulic motors (31 to 34), each with a fixed displacement, wherein the displacement of the assembly is hydraulically modified by valves (88, 85) in a range limited by the maximum displacement of all fixed displacement motors (31 to 34) and a non-zero minimum displacement, each of these hydraulic motors (31 to 34) being connected to one wheel of the vehicle (11 to 14) via disengagement means (21 to 24), allowing disengagement of the wheels depending on the variation of the assembly displacement.
Another object of the invention is a circuit for controlling a vehicle of this type in such a way that the actions performed by the driver are continually monitored and controlled by the control circuit to optimize operating conditions and energy regeneration of the vehicle.
This object is attained by the fact that the circuit which monitors and controls the angle of the cam plate which controls the variable displacement of the pump, receives on the one hand information indicating the pressure of the fluid between the pump and the hydraulic motor, and on the other hand, information indicating either the current discharged by the battery to the electrical motor during the driving phases either of the current generated by the electrical motor during braking or deceleration phases and uses this information to correct the control signal of the angle of the cam plate as a function of the reference threshold values.
According to another characteristic, the reference threshold values set by the circuit which monitors, manages and controls the angle of the cam plate allow the battery to be recharged during braking or deceleration phases of the vehicle.
According to another characteristic, the circuit which manages the control voltage of the cam plate determining the pump displacement variation receives a signal indicating the degree to which the accelerator is depressed, a signal from a switch indicating forward or reverse motion of the vehicle, a signal indicating the actuation of the brake pedal, a signal generated by a first circuit which indicates enabling of forward/backward motion of the vehicle and a signal generated by a second circuit indicating the maintenance of the control voltage for the management circuit to limit variation of the control voltage.
Another characteristic is the output of an xe2x80x9cORxe2x80x9d logic circuit with three inputs, one input of which receives a signal indicating the charge state of the battery;
another input receives a signal indicating the current discharged or received by the battery;
the third input receives a signal indicating the pressure of the fluid between the pump and the motor compared to a maximum reference pressure.
According to another characteristic, the pressure signal is delivered by the output of a comparator, receiving at one of its inputs the signal from the pressure sensor originating from the circuit between the pump and the hydraulic motor, and on the other hand a reference voltage indicating maximum pressure.
According to another characteristic, the circuit generating the signal indicating the charge current generated by the electric motor to the battery or the current discharged by the battery in the electric motor is comprised of a comparator which receives at one of its inputs the output signal of an amplifier of the absolute value of the current measured by a current loop sensor, and at its second input a signal indicating a reference current I0, I1, I2 which will depend on detection of the polarity on the one hand, and on the other hand, detection of actuation of the brakes.
According to another characteristic, polarity is detected by a polarity detector circuit which actuates during detection of a reversal in the direction of the current signalling charging of the battery, actuation of a switch enabling the power supply voltage of the electronic circuit to be switched from a first position powering a first element which generates a first signal indicating first maximum current I0 allowable by the electric motor, to a second position powering a second element which generates a second signal indicating second current I1 corresponding to a vehicle deceleration current.
According to another characteristic, the brake actuation detection switch controls the changeover switch for the power supply voltage of the electronic circuit on a third circuit providing a voltage indicating a fixed or variable vehicle braking current I2.
According to another characteristic, the electric motor is of the direct current and parallel excitation type.
According to another characteristic, the electric motor is of the alternating current and synchronous or asynchronous type and the electrical power supply circuit from the battery includes a current inverter.